Removal of heavy metals in medical waste incineration fly ash by Na2EDTA combined with zero-valent iron and recycle of Na2EDTA: Acolumnar experiment study

In this study, an effective circulating system was developed to remove heavy metals in medical waste incineration (MWI) fly ash. MWI fly ash (MWIFA)-column experiments were performed to remove Cu, Pb, Zn, Cd, and Ni from MWIFA using EDTA disodium (Na(2)EDTA). Iron-column experiments were conducted to study the removal effect of zero-valent iron on the five heavy metals from washing wastewater. Toxicity Characteristic Leaching Procedure (TCLP) test method was employed to evaluate heavy metals toxicity of MWIFA residues generated after 0-0.2 mol/L Na(2)EDTA solution treated. After being washed by 0.2 mol/L Na(2)EDTA solution, TCLP leaching values of Cu, Pb, Zn, Cd, and Ni were the lowest and satisfied the standard (GB 5085.3-2007), and the leaching values were 58.4 +/- 2.0 mg/L, 2.81 +/- 0.14 mg/L, 64.3 +/- 4.0 mg/L, 0.156 +/- 0.005 mg/L, 0.381 +/- 0.006 mg/L. Concentrations of Cu, Pb, Zn, Cd, and Ni in iron-column effluent were reduced by 99.7%, 91.6%, 91.6%, 75.4%, and 75.7%, respectively. Na(2)EDTA was recovered and recycled to the removal of heavy metals from MWIFA. Comparing new Na(2)EDTA solution with recycled Na(2)EDTA solution, recycled Na(2)EDTA and water could be reutilized to dispose MWIFA. The removal efficiencies of Cu, Pb, Zn, Cd, and Ni by recycled 0.2 mol/L Na(2)EDTA solution were 67.1%, 68.8%, 63.2%, 73.9%, 50.7%, respectively, the removal efficiencies using recovered Na(2)EDTA decreased by 2.6%, 3.9%, 3.3%, 4.2%, and 1.6%, respectively. Successive batch experiments were also conducted to evaluate industrialization potential and reusable times for recycled Na(2)EDTA. After four recirculation cycles, extraction efficiencies of Pb and Cd (removal efficiency at different cycles divided by removal efficiency of new Na(2)EDTA) declined toward 80%. Results from this research indicated that this circulating system possessed industrialization potential. Implications An effective circulating system was developed to remove heavy metals in MWI fly ash (MWIFA). Integration of Na(2)EDTA with Fe(0)promoted the removal of heavy metals from MWIFA. Na(2)EDTA, NaCl and water were stepwise extracted from iron-column effluent, respectively. Recovered Na(2)EDTA can still effectively remove heavy metals from MWIFA. Results from this research indicated that this circulating system possessed industrialization potential.